Submerged membranes are used to treat liquids containing solids to produce a filtered liquid lean in solids and an unfiltered retentate rich in solids. For example, submerged membranes are used to withdraw substantially clean water from wastewater and to withdraw potable water from well water or surface water.
Immersed membranes are generally arranged in modules which comprise the membranes and headers attached to the membranes. The modules are immersed in a tank of water containing solids. A transmembrane pressure (“TMP”) is applied across the membrane walls which causes filtered water to permeate through the membrane walls. Solids are rejected by the membranes and remain in the tank water to be biologically or chemically treated or drained from the tank.
U.S. Pat. No. 5,639,373, issued to Zenon Environmental Inc. on Jun. 17, 1997, describes one such module using hollow fibre membranes. In this module, hollow fibre membranes are held in fluid communication with a pair of vertically spaced headers. TMP is provided by suction on the lumens of the fibres through the headers. Other modules are shown in U.S. Pat. No. 5,783,083 issued to Zenon Environmental Inc. on Jul. 21, 1998, PCT Publication No. WO 98/28066 filed on Dec. 18, 1997 by Memtec America Corporation and European Patent Application No. EP 0 931 582 filed Aug. 22, 1997 by Mitsubishi Rayon Co., Ltd. As discussed in these documents, various means are provided for fixing modules together generally permanently into larger units.